** Vertex angle, vertex of an angle**

**Vertex angle **the angle that is formed by two lines crossing at a vertex.

An angle associated with a vertex of a polygon.

A vertex angle is measured in degrees.

**Vertex angles of regular polygons**

**Angle formulas for regular polygons**

**n – the number of sides**

**Vertex angle of an isosceles triangle**

In an isosceles triangle, the **apex is the vertex** where the two sides of equal length meet, opposite the unequal third side.

The angles at the base are called the **base angles,** and the angle opposite the base is called the **vertex angle.**